Camilo Tello

Galactic foreground contribution to the BEAST cosmic microwave background anisotropy maps

We report limits on the Galactic foreground emission contribution to the Background Emission Anisotropy Scanning Telescope (BEAST) Ka- and Q-band CMB anisotropy maps. We estimate the contribution from the cross-correlations between these maps and the foreground emission templates of an H? map, a destriped version of the Haslam et al. 408 MHz map, and a combined 100 ?m IRAS DIRBE map. Our analysis samples the BEAST ~10? declination band into 24 one-hour (R.A.) wide sectors with ~7900 pixels each, where we calculate (1) the linear correlation coefficient between the anisotropy maps and the templates; (2) the coupling constants between the specific intensity units of the templates and the antenna temperature at the BEAST frequencies; and (3) the individual foreground contributions to the BEAST anisotropy maps. The peak sector contributions of the contaminants in the Ka-band are of 56.5% free-free with a coupling constant of 8.3 ? 0.4 ?K R-1, and 67.4% dust with 45.0 ? 2.0 ?K MJy-1 sr-1. In the Q band the corresponding values are of 64.4% free-free with 4.1 ? 0.2 ?K R-1 and 67.5% dust with 24.0 ? 1.0 ?K MJy-1 sr-1. Using a lower limit of 10% in the relative uncertainty of the coupling constants, we can constrain the sector contributions of each contaminant in both maps to <20% in 21 (free-free), 19 (dust), and 22 (synchrotron) sectors. At this level, all these sectors are found outside of the b = 146 region. By performing the same correlation analysis as a function of Galactic scale height, we conclude that the region within b = ?175 should be removed from the BEAST maps for CMB studies in order to keep individual Galactic contributions below ~1% of the maps rms.

The Cosmic Microwave Background Anisotropy Power Spectrum from the BEAST Experiment

The Background Emission Anisotropy Scanning Telescope (BEAST) is a 2.2 m off-axis telescope with an eightelement mixed Q-band (38–45 GHz) and Ka-band (26–36 GHz) focal plane, designed for balloon-borne and ground-basedstudiesofthe cosmicmicrowavebackground(CMB).Herewepresentthe CMB angularpowerspectrumcalculatedfrom682hrofdataobservedwiththeBEASTinstrument.Weuseabinnedpseudo-Cl estimator(the MASTER method). We find results that are consistent with other determinations of the CMB anisotropy for angular wavenumbers l between 100 and 600. We also perform cosmological parameter estimation. The BEAST data alone produce a good constraint on k � 1 � tot ¼� 0:074 � 0:070, consistent with a flat universe. A joint parameter estimation analysis with a number of previous CMB experiments produces results consistent with previous determinations. Subject heading gs: cosmicmicrowavebackground — cosmology:observations — large-scalestructureofuniverse

The Optical Design of the Background Emission Anisotropy Scanning Telescope (BEAST)

We present the optical design of the Background Emission Anisotropy Scanning Telescope (BEAST), an offaxis Gregorian telescope designed to measure the angular distribution of the cosmic microwave background radiation (CMBR)at30and 41.5 GHzonangularscalesrangingfrom 20 0 to10 � .Theapertureof thetelescope is1.9m, and our design meets the strict requirements imposed by the scientific goals of the mission: the beam size is 20 0 at 41.5 GHz and 26 0 at 30 GHz, while the illumination at the edge of the mirrors is lower than � 30 dB for the central horn.Theprimarymirror isanoff-axissectionofaparaboloid,andthesecondaryanoff-axissectionofanellipsoid.A spinning flat mirror located between the sky and the primary provides a two-dimensional chop by rotating the beams around an ellipse on the sky. BEAST uses a receiver array of cryogenic low noise InP High Electron Mobility Transistor (HEMT) amplifiers. The baseline array has seven horns matched to one amplifier each and one horn matchedtotwoamplifiers(twopolarizations)foratotalofnineamplifiers.Twohornsoperatearound30GHz,andsix operate around 41.5 GHz. Subsequent campaigns will include 90 GHz and higher frequency channels. Subject heading gs: cosmic microwave background — cosmology: observations — telescopes

Spillover and diffraction sidelobe contamination in a double-shielded experiment for mapping Galactic synchrotron emission

We have analyzed observations from a radioas- tronomical experiment to survey the sky at decimetric wavelengths along with feed pattern measurements in or- der to account for the level of ground contamination enter- ing the sidelobes. A major asset of the experiment is the use of a wire mesh fence around the rim-halo shielded an- tenna with the purpose of levelling out and reducing this source of stray radiation for zenith-centered 1-rpm circu- lar scans. We investigate the shielding performance of the experiment by means of a geometric diraction model in order to predict the level of the spillover and diraction sidelobes in the direction of the ground. Using 408 MHz and 1465 MHz feed measurements, the model shows how a weakly-diracting and unshielded antenna conguration becomes strongly-diracting and double-shielded as far- eld diraction eects give way to near-eld ones. Due to the asymmetric response of the feeds, the orientation of their radiation elds with respect to the secondary must be known a priori before comparing model predictions with observational data. By adjusting the attenuation coe- cient of the wire mesh the model is able to reproduce the amount of dierential ground pick-up observed during test measurements at 1465 MHz.

The 2.3 GHz continuum survey of the GEM project

Context. Determining the spectral and spatial characteristics of th e radio continuum of our Galaxy is an experimentally challenging endeavour for improving our understanding of the astrophysics of the interestellar medium. This knowledge has also become of paramount significance for cosmology, since Galactic emiss ion is the main source of astrophysical contamination in measurements of the Cosmic Microwave Background radiation. Aims. In this paper we present the scope of the Galactic Emission Mapping (GEM) project and its results at 2.3 GHz. Its observational program was conceived and developed to reveal the large scale properties of Galactic synchrotron radiation in total int ensity and polarisation through a self-consistent set of radio contin uum surveys between 408 MHz and 10 GHz. GEM’s unique observational strategy and experimental design aim at the production of foreground templates in order to address the mutual inconsistencies between existing surveys. Methods. The GEM experiment uses a portable and double-shielded 5.5-m radiotelescope on a rotating platform to map 60 ◦ wide declination bands, from different observational sites, by circularly scanning the sky a t 30 ◦ from the Zenith. The observations at 2.3 GHz were accomplished with a total power receiver, whose front-end HEMT was matched directly to a cylindrical horn at the prime focus of a parabolic reflector. The Moon was used to cali brate the antenna temperature scale and the preparation of the map required direct subtraction and destriping algorithms to r emove ground contamination as the most significant source of systematic error. Results. For this first GEM survey, 484 hours of observations were used from two locations in Colombia and Brazil to yield a 69% sky coverage fromδ =−53 ◦ toδ = +35 ◦ with a horizontal HPBW of 2. 30 and a vertical HPBW 1. ◦ 85. The pointing accuracy was 8. 6 and the RMS sensitivity was 9.8± 1.6 mK. The zero-level uncertainty is 103 mK with a temperature scale error of 5% after direct correlation with the Rhodes/HartRAO survey at 2326 MHz on a T -T plot.